Highly viscous materials, such as adhesives, sealants, and the like may be packaged within drums for storage and shipment, and while such materials are flowable at elevated temperatures, the materials are substantially solid at normal ambient temperatures and require reheating prior to usage. For instance, such thermoplastic adhesives are widely used for assembly purposes in the automobile and construction arts, and sealants of this type are often employed in the fabrication of multiple pane window units.
Dispensing apparatus for highly viscous hot melt materials have been developed by the assignee, and others, and normally include a head or platen which is received within the material drum for engagement with the surface of the material. The platen is heated causing the material adjacent thereto to melt and become flowable, and a pump mounted upon an elevating apparatus includes an inlet adjacent the platen wherein the melted material may be drawn into the pump and dispensed through a distribution system, such as a heated hose line and nozzle. The nozzle may be hand held and operated by a manual lever controlling a valve wherein opening of the valve permits dispensing.
Operation of the pump is usually through an expansible chamber motor operated by compressed air. Accordingly, the reciprocal movements of the air motor piston and piston rod are transmitted to a pump piston rod and piston causing the pump to draw melted material into its chamber during piston rod retraction, and forcing material from the pump chamber during extension of the air motor piston rod.
As such combination expansible chamber pump and motor units are powered by compressed air, and as the compressed air pressure within the air motor is at a relatively high dispensing pressure when the dispensing nozzle valve is closed, a surge of material is expelled from the nozzle when its valve is initially opened. It is necessary to maintain a relatively high pressure within the air motor during dispensing to produce the desired rate of flow, but the air pressures existing within the air motor when the dispensing valve is closed are such as to usually produce a surge of material ejected from the nozzle when the nozzle is opened causing excess material to be dispensed which may result in defects and unsightly material deposits, and cause an uneven material distribution which may result in leakage or other serious problems.
When the dispensing valve is closed the air motor and pump will "stall out" and become immobilized due to the lack of material flow and the components will be under the relatively high pressure required for dispensing. This condition causes fatigue on the motor, pump and valve components, as well as produces the initial material surge, and is objectionable as it shortens the life of the equipment.
Apparatus such as that described above is generally represented in U.S. Pat. Nos. 3,412,903 and 3,976,229, and in such apparatus surging and high pressure stalling will occur.
Further, in prior art dispensing equipment, if multiple dispensing heads are being supplied from a single pump the pressure upon the air motor must be increased in order to maintain the desired quantity of flow through each head, and in such a system the presence of such high air motor pressures results in even more serious surge problems, especially if the dispensing nozzles are not simultaneously operated.
It is an object of the invention to provide a dispensing system for viscous materials utilizing a compressed air expansible motor operated pump wherein material flow surges are eliminated during start and stop operations.
A further object of the invention is to provide a dispensing system for viscous materials pumped by a compressed air operated motor wherein material flow surges are eliminated during the initial stage of material flow and wherein a substantially uniform flow of material is maintained during dispensing.
Another object of the invention is to provide a compressed air controlled dispensing system for viscous materials wherein variable air pressures control dispensing dependent upon the condition of a material flow control valve.
Another object of the invention is to provide a compressed air powered dispensing system for viscous materials wherein a plurality of dispensing nozzles or heads are provided from a single pump, and wherein variable air pressures are imposed upon the pump drive motor dependent upon the condition of the dispensing valves whereby a minimum air pressure is utilized when no dispensing is occurring, an intermediate air pressure is supplied to the pump motor when dispensing through a single nozzle is occurring, and a maximum air pressure is supplied to the pump air motor when a plurality of nozzles are dispensing to provide a uniform and equal material flow through each nozzle.
Yet another object of the invention is to provide a compressed air controlled dispensing system for viscous material utilizing a plurality of dispensing nozzles supplied from a common compressed air powered pump wherein flow surges from the nozzles are prevented by controlling the pressure within the pump dependent upon the operation of the dispensing nozzles, and wherein operation of the dispensing nozzles may not be simultaneous, but may be intermittent or sequential.
In the practice of the invention an expansible chamber pump utilizing a piston mounted upon a piston rod is operated by an expansible chamber air motor employing a piston rod common or connected to the pump rod mounted upon a piston within the air motor. The air motor is connected to a compressed air source and valved to reciprocate causing the pump piston to reciprocate for alternately drawing material into the pump chamber and expelling the same therefrom. The pump communicates with a source of viscous material, such as a hot melt adhesive or sealant, drawing the material into the pump chamber as the pump chamber increases in volume, and the material is forced from the pump chamber into a heated hose line as the pump chamber volume is reduced.
The pumped material is dispensed through a valved nozzle or head, usually heated, wherein the material is discharged when the valve is opened, and dispensing ceases upon the valve closing. If the dispensing nozzle is in the form of a hand held gun a manually operated trigger lever is normally employed to control the position of the valve.
A compressed air source communicates with an air pressure control system including at least two air pressure regulators communicating with a valve controlling flow to the air motor. One of the regulators produces a low pressure output, while the output of the other regulator is significantly higher. Both regulators communicate with a solenoid operated three way valve communicating with the pump air motor which determines which of the regulators are supplying compressed air thereto.
An electric switch is associated with the valve at the dispensing nozzle wherein opening of the valve to dispense pumped material closes the switch, while closing of the dispensing valve opens the switch contacts. As the shifting of the solenoid operated valve is controlled by the electric switch at the dispensing nozzle it will be appreciated that selectivity of high and low air pressures to the air motor is dependent upon the position of the nozzle valve.
In order to eliminate material flow surges, closing of the dispensing valve shifts the solenoid valve to the position which establishes communication between the low air pressure regulator and the air motor. Thus, a low "stall" pressure is imposed upon the air motor and pump when dispensing is not occurring. Opening of the dispensing valve will close the electric switch shifting the solenoid valve to the position permitting higher pressure compressed air to be introduced into the pump air motor to provide the necessary pumping force and flow of material through the nozzle to achieve the desired dispensing characteristics. Accordingly, it will be appreciated that higher pressure compressed air is only introduced into the pump air motor during dispensing, and a lower air pressure is imposed on the pump air motor when dispensing is not occurring. Thus, when the dispensing valve is initially opened the reduced pressure upon the pumped material will not cause a surge of material to be expelled from the dispensing nozzle and a much more uniform flow from the nozzle is achieved during the stop and start sequences of dispensing.
In those instances wherein a plurality of dispensing nozzles are supplied from a common pump, for instance, it is not uncommon for two dispensing nozzles to be connected to a single pump, it is also possible to utilize the concepts of the invention. In multiple dispensing nozzle or head systems wherein the dispensing nozzles normally operate intermittently and randomly, rather than simultaneously, additional compressed air regulators are used to provide higher air pressures at the pump air motor dependent upon the amount of material being pumped at a given time.
For instance, a third air regulator is included in the air control system having a compressed air output pressure higher than that of the higher air pressure regulator used in a dispensing system employing only a single nozzle. In such instance, the solenoid controlled valve includes additional control passages, or may constitute a second solenoid control valve which selectively communicates with the three air regulators, and determines whether a low stall pressure, intermediate pressure, or high air pressure is transmitted to the pump air motor.
Each of the two dispensing nozzles includes a valve and electric switch associated therewith, and the electric switches are connected in parallel with respect to the solenoid operated valve means wherein opening of either dispensing nozzle will shift the solenoid operated valve means from the low stall pressure flow path to the pump air motor to the higher intermediate air pressure required to permit the desired dispensing through a single nozzle. The dispensing nozzle electric switches are also connected in series to the solenoid valve means wherein the highest air pressure is supplied to the pump air motor if both dispensing nozzles are open, and in such instance the air supplied to the pump and motor is sufficient to substantially double the flow of dispensed material to achieve the desired flow rates at both nozzles.
Accordingly, the air pressure supplied to the pump air motor will be controlled in accord with the pumping pressures required to achieve optimum dispensing characteristics of the viscous material, and yet, surging of the material will be eliminated. A further advantage of the invention over conventional dispensing systems results from the extended life of the components due to a reduction in fatigue pressures because of the elimination of high static stall-out pressures.